The invention relates to a semiconductor device having an integrated circuit comprising a substrate of a first conductivity type and an epitaxial layer which is present thereon, and which is divided into islands of the second, opposite conductivity type which are surrounded laterally by a surrounding region of the first conductivity type, a bipolar transistor being provided in at least one island.
The invention relates in addition to a method of manufacturing the semiconductor device.
Conventional monolithic integrated circuits show the above-described structure.
In the ever-progressing integration of semiconductor circuits the dimension of the individual semiconductor circuit elements and their mutual distance become smaller and smaller. The packing density to be realized is determined to an ever more important extent by the technology used. In known integrated circuits of the kind mentioned above, for example, the minimum width of the surrounding region between the islands is mainly determined by the lateral diffusion which occurs in the usual isolation diffusions which in the known monolithic integrated circuits form the said surrounding region.
A further limit on the compactness of the structure is imposed by the fact that the buried collector layer generally remains at a certain distance from the isolation diffusion in order to avoid a severe reduction of the breakdown voltage.
In addition to the packing density, the switching speed in highly integrated circuits is of great importance. This speed must generally be as high as possible.
A further important point is the power dissipation. Particularly in circuits comprising memories, low power dissipation with high switching speed is of importance.
These conditions are not realized simultaneously with known technologies in which the islands are formed by homogeneously doped portions of the epitaxial layer which are separated by isolation diffusions.